Polymer-supported salen complexes for heterogeneous asymmetric synthesis: Stability and selectivity

The enantioselectivity of the manganese-salen complex in the epoxidation of unfunctionalized olefins and the influence of grafting

“…This mostly led to a decrease in selectivity unless there was no covalent interaction between the complex and the host, allowing a high freedom of movement [30]. One possible approach to immobilizing the complex is building it up piece by piece on the solid support, as reported by Angelino et al [28,29] In this paper a similar approach is used anchoring the catalyst on a chloromethylated MIL-101.…”

Polymer-Supported (Salen)Mn Catalysts for Asymmetric Epoxidation: A Comparison between Soluble and Insoluble Matrices

“…With each of the soluble polymer-bound catalysts, a color change from dark brown to a lighter shade of brown was observed with each successive use. This likely results from leaching of manganese caused by oxidative degradation of the salen ligand, a problem that has been documented by others with insoluble supported catalysts. 7c,d …”

“…The enantioselectivities derived from the soluble and J anda J el polymeric catalysts were nearly equivalent to those for the commercial catalyst 1 ; however, only the J anda J el-bound complex 7 could be used for as many as three cycles. Apparently, oxidative decomposition over repeated use gradually renders the catalyst inactive, as has been noted previously. 7c,d This inability to recycle the catalysts indefinitely appears to be a fundamental limitation of salen-based oxidation catalysts which is difficult to overcome without sacrificing enantioselectivity. Nevertheless, the J anda J el-bound catalyst described herein provides the highest ee to date for epoxidation catalysts attached to gel-type resins and may find utility in high-throughput organic synthesis since they simplify product purification.…”

“…It has been established that the commercial catalyst 1 is unstable to prolonged oxidative conditions and cannot be recycled . Laibinis has reported that supported (salen)Mn complexes are also susceptible to decomposition; however, these reactions were carried out at room temperature for prolonged times (20 h). 7c,d We hoped that the short reaction times and low temperatures used in our studies would prevent or at least slow catalyst degradation. As each of the tested catalysts displayed adequate selectivity, attention was next turned to examining their recovery and reuse.…”

Organo-Laponites as Novel Mesoporous Supports for Manganese(III) salen Catalysts

“…The comparison with results from literature, obtained with other matrixes as natural montmorillonite clays, silicas or polymeric supports 13,21,[35][36][37] is not straightforward. However, we believe that the methodology described in this work can be of interest for the immobilization of large complexes.…”